请用英语回答：What is "cash flow"?

请用英语回答：What is "cash flow"? what is the operating cash flow? cash-flow 原题：What is the present value of an infinite set of cash flow why cash flow is important to company cash net cash flow difference what fruit is never find singly?请用英语回答? cash flow hedge是什么意思 cash flow statement discounted cash flow [英语]The UN is short of cash.请用英语解释该句子 What is a cash register?